It is known to make reinforcing mats from glass fibers and to use these mats as substrates in the manufacture of a large number of roofing products. Any known method of making nonwoven mats can be used, such as the conventional wet laid processes described in U.S. Pat. Nos. 4,112,174, 4,681,802 and 4,810,576, the disclosures of which are incorporated herein by reference. In these processes a slurry of glass fiber is made by adding glass fiber to a typical white water in a pulper to disperse the fiber in the white water forming a slurry having a fiber concentration of about 0.2-1.0 weight %, metering the slurry into a flow of white water to dilute the fiber concentration to 0.1 or below, and depositing this mixture on to a moving screen forming wire to dewater and form a wet nonwoven fibrous mat.
This wet nonwoven mat of glass fiber is then transferred to a second moving screen and run through a binder application saturating station where an aqueous binder mixture, such as an aqueous urea formaldehyde (UF) resin based binder mixture, is applied to the mat in any one of several known ways. The binder saturated mat is then run over a suction section while still on the moving screen to remove excess binder. The wet mat is then transferred to a wire mesh moving belt and run through an oven to dry the wet mat and to cure (polymerize) the UF based resin binder which bonds the fibers together in the mat. Preferably, the aqueous binder solution is applied using a curtain coater or a dip and squeeze applicator, but other methods of application such as spraying will also work.
In the drying and curing oven the mat is subjected to temperatures up to 450 or 500 degrees F. for periods usually not exceeding 1-2 minutes and as little as a few seconds. Alternative forming methods include the use of well known processes of cylinder forming, continuous strand mat forming which lays continuous strands of glass fibers in overlapping swirls, and "dry laying" using carding or random fiber distribution.
UF resins, usually modified with one or more of acrylic, styrene butadiene, or vinyl acetate resins, are most commonly used as a binder for fiber glass mats because of their suitability for the applications and their relatively low cost. Melamine formaldehyde resins are sometimes used for higher temperature and/or chemical resistant applications. To improve the toughness of the mats, a combination of higher mat tear strength and mat flexibility, which is needed to permit higher processing speeds on roofing product manufacturing lines and for maximum roofing product performance on the roofs and in other applications, it is common to modify or plasticize the UF resins as described above.
Mats made in the above described manner perform well in many applications, but do not provide the bonding strength desired for bonding to wood products.